Alloy addition agent



Patented Feb. 17, 1953 ALLOY ADDITION AGENT Donald C. Hilty, NiagaraFalls, N. Y., assignor to Union Carbide and Carbon Corporation, acorporation of New York No Drawing. Application November 3, 1951, SerialNo. 254,796

6 Claims.

The invention relates to a method and agent for incorporating alloyingelements into molten iron or steel and for adding heat to molten ironand steel to facilitate the addition of alloying elements to suchmetals.

It is 'well known that the addition of ferroalloys such as ferrochromiumto steel or cast iron can be greatly facilitated by incorporating withthe ferro-alloy an exothermic mixture which, upon addition to molteniron or steel, will react, liberating heat. This heat raises thetemperature and heat content of the ferro-alloy, thereby reducing thechilling effect that normally accompanics the addition of such alloys tomolten iron or steel. The advantages of these exothermic agents havelong been recognized by those skilled iii the steelmaking art.

' ZCustomarily, these agents are prepared by pelleting or briquettingintimate mixtures of finely domminuted fero-alloy, a reducing agent, andan oxidizing agent. The reducing agent may be added separately or may bea component of the ferro-alloy. The pellets or briquets may be bonded inany of a number of different ways depend- .fijng on the nature of theconstituents or on other factors.

It will be evident that many combinations of oxidizing and reducingagents are possible, the choice being dictated by considerations ofthermal efiiciency, the specific ferro-alloys involved, economy,undesirable side reactions, and other factors.

It has been proposed, for example, by Udy in U. S. Patent No. 2,280,875to introduce chromium into iron or steelby igniting in contact with theiron or steel in the molten state an exothermic reaction mixturecomprising high-carbon ferrochromium, silicon-containing material, andsolid oxidizing material capable of reacting exothermically with carbonand silicon. In this mixture the components are present in such amountsand proportions as to effect, upon ignition of the reaction mixture,oxidation and elimination of a portion of the carbonof the ferrochromiumthrough reaction with the oxidizing material in an amount sufiicient toproduce a substantial exothermic effect. Udy proposes as the oxidizingmaterial an alkali metal nitrate, alkali metal chlorate, or alkali metalchromate.

In any exothermic addition agents of this type, exothermicity alone isnot enough to assure the effectiveness of the agent. In order to besatisfactory for the addition of ferro-alloys to steel, such agents mustnot only generate at least a part of their own heat of solution but mustdissolve readily in the molten metal. Unless rapid solution occurs, poorrecovery of the ferro-alloy addition and bad segregation of the alloy inthe steel result. It will be evident, therefore, that exothermicity andhigh rate of solution are complementary, and that one of the mostimportant criteria for judging the effectiveness of these exothermicmixtures is rate of solution.

Potassium perchlorate is a powerful oxidizing agent, and bythermodynamics it can be shown that the oxidation of silicon bypotassium perchlorate is potentially very strongly exothermic.Practically, however, under the conditions prevailing for the additionof ferro-alloys to steel, the reaction is difficult to initiate andpropagate. This has been demonstrated by tests wherein pelleted mixturesof 100 mesh (0.0059 inch openings) 75% ferrosili'con and potassiumperchlorate in stoichiometric proportions were added to molten seel inan induction furnace. The pellets merely floated on the surface of thesteel with no visible signs of reaction and dissolved in the steel onlyvery slowly if at all.

It is an object of the present invention to pro vide a mixture whereinpotassium perchlorate and silicon may be reacted to provideexothermicity for introducing alloying elements into molten iron andsteel.

Another object is to provide a mixture which will greatly increase therate of solution of alloying materials in molten iron or steel.

Still another object is to provide such a mixture wherein carbon isessentially unoxidized in the reaction and, if present, may beintroduced as an alloying element into the molten iron or steel.

A still further object is to provide a method of heating molten iron orsteel by the use of the reaction mixture of the invention so as tofacilitate the addition of alloying elements to such metals.

The present invention is based upon the discovery that by the additionof an accelerator which promotes the reaction between silicon andpotassium perchlorate, such as sodium carbonate conveniently availableas soda ash, to the potentially strong but otherwise difiicultlyreactable reaction mixture of silicon and potassium perchlorate, acontrolled chemical reaction evolving considerable heat is produced.When the reaction is applied by adding a mixture; suitably in pellets,of silicon, potassium'perchlorate, and soda ash to molten iron andsteel, for example, heat is transferred to the molten metal permittingthe addition of alloying elements without detrimentally chilling themetal. When the reaction is applied to ferro-alloys by incorporating thesilicon, potasium perchlorate, and soda ash in mixtures of ferro-alloys,either pelleted or unpelleted, the solution of the alloys in molten ironand steel is greatly improved.

When potassium perchlorate and silicon are pelleted with finelycomminuted ferro-alloys such as ferrochromium, they are not especiallyhelpful and, in fact, may retard solution of the alloy in steel.Moreover, although potassium perchlorate will readily reactexothermically with carbon or ferro-alloys containing carbon, as forexample high-carbon ferrochrome, this exothermic :reaction .does notmeasurably improve the rate of'solutioniof the ferro-alloy in steel.When, however, .a combination of silicon, potassium perchlorate, and anaccelerator such as soda ash is employed as the-active ingredient, theresult is not only a high degree of exothermicity, as will be shownlater in this'specification, but an outstanding improvement in the rateof solution of the ferro-alloy. These efiects are illustrated by theresults of rate-of-solution tests liste in Table I.

The test procedure for making the rate-o'f-solution tests was asfollows: A 1'00-lb. heat of steel was melted'in an induction furnace andbrought to a temperature of approximately 1600 C. A pelleted mixture ofa measured'quantity of ferroalloy, in this case 100grams of chromium ashighcarbon 'ferrochrome, and the active ingredients as specified, wasadded to the surface of the molten metal. The time'necessary for thedisappearance of the last vestiges of the addition was measured by stopwatch and is considered to bean index of the solubility rate of thepellet. In Table I, theeffect ofeven a small amount of soda ash isnotable. The pellets employed for these tests and subsequenttestsdescribed in this specification were made bymixing the metallicconstituents, 100 mesh by down in particle size, withpotassiumperchlorate and soda ash. .No special sizing of the potassiumperchlorate and soda ash wasemployed, these agents being used in thefairly finely divided form normally available commercially. Mixing wasaccomplishedby briefly shaking the constituents together after whichwater was added to the mixture until the particles would stick together.The mixture'was then compressed into cylindrical pellets '1 2/2 inchesin diameter and 1% to 2 /zinches long, on a-hydraulic'press atapproximately 4000 p. s. i. The pellets were then dried in an oven atTABLE I Efiect of accelerator on rate of solution Composition ofPellets, Percent Accele- Time to High- Potasmm D's ol Ferro- 757 (SodaLS 23?: chrome Eerr o- Ash) Seconds chrome Silicon silicon chlorate 10060 95 5 5i 92.5 7.5 65 90 10 61 90 5 5 75 89 5 5 1 32 88 5 6 2 36 N 87 5W 5 3 36 86 5 '5 4 31 5 .5 5 33 r ,In order that the mechanism of theinvention may be more fully understood tests have been made whichdemonstrate (1) that an accelerator such as sodaash is essential forobtaining an effective reaction between silicon contained in theconstitutents of the mix and potassium perchlorate for bothhighandlow-silicon alloys; (2)

that'with the accelerator present in accordance with the invention,silicon is oxidized in preference to carbon, so that when sufficientsilicon is present to react with the potassium perchlorate, the carbon.is unaffected and remains available for solution in the steel; and (3)that when carbon is present in the absence of an accelerator, carbon isoxidized as taught in the prior art by Udy even if siliconbe present inan amount sufiicient for reaction with all of'the potassium perchlorate.

, In these tests pelleted mixtures of ferrochromium (highandlow-carbon), low-carbon ferrochromium-silicon, potassium perchlorate,and soda ash were prepared in which the pellets had the compositionshown inTable II.

TABLE II Percent Pellet Potessi-. Carbon Silicon f um per- "Soda ashchlorate l 4.79 .5.06 62.2 5.0 ..L 4174 J5.60 130.3 .5. '0. L210 T5. 57269. 3; 5. 0 2.0 5.69; 60.5 =5.'0

1 Includes carbon in soda. ash.

Pellets A and B were tested "by the solubility test procedure'previouslydescribed in this specification with the-resultsindicated'below in TableIII.

B (containing5% soda ash as'accelerator), 34 seconds.

The effect of the accelerator in pellet B in promoting thereactionzand-.solution in steel of these highesiliconpellets ismanifest. -Without the .accelerator,-.as shown :by pellet A, :themixture was non=reactive:andcdidnot dissolveatall.

Pellets 'C, D, E, and F were subjected to excthermicity tests. Thesetests were made by operating a IOU-pound capacity induction furnace as acalorimeter. A heat of steel was melted down, thoroughly de-oxidizedwith manganese, silicon and aluminum, and raised to a temperature of1600 C. The power input to the furnace was then adjusted so that it wasjust sufiicient to maintain the molten metal at constant temperature.When it was certain that constant temperature was being maintained; i.e., when the heat showed no measurable temperature variation for aperiod of at least 5 minutes, a quantity of the specified pelletedmixture sufiicient to add 1% chrominum to the steel was added. Thetemperature of the heat was then observed until it again became constantat a new level. Temperatures were measured by means of a platinum vs.platinum plus rhodium thermocouple encased in a refractory sheathcontinuously immersed in the steel bath. The difference between theconstant temperatures at the beginning and end of the test wasconsidered to be a measure of the exothermic character of the pellets.The results of the tests are reliable comparisons of the relativechilling effects of the various addition agents on molten steel. Samplesof the steel were taken from the test heats immediately before andimmediately after the pellet additions, and analyzed so that therelative oxidation and recovery of carbon and silicon could bedetermined. The results of these tests are shown in Table IV.

The exothermic action of the potassium perchlorate-silicon-soda ashmixture in reducing the heat loss accompanying the addition of aferro-alloy such as ferrochromium to molten steel is illustrated byTable V. Table V contains the results of measurements of the temperaturechange produced in 100-lb. heats of steel by the introduction of 1%chromium in the form of the various pelleted mixtures. These tests wereconducted in the same manner as the tests shown in Table IV.

The silicon in the mixture of the invention which contains an elem nt tohe alloyed with iron or steel must be at least sufiicient to combinewith all of the oxygen in the potassium perchlorate. An excess of oxygenwill result in TABLE IV Composition of Steel, Percent Temp Solubi- Dre 03 1 Pellet i iiii le g? i l il I Ch Alcntifiaollv (102.0. Pe ct e et vange Recovery mom Addition Addition if fi C-C0ntaining no accel- C 0.015 0.085 0.070 0.077 90.9 erator 17 76 Si 0. 240 0. 264 0. 024 0 081 297 Cr 0. ()l 0. 97 0. 96 0. 99 97. 0 DOcntaining 2% soda C 0. 014 0. 0900.076 0.076 1000 h 9 34 Si 0. 133 0. 148 0. 015 0. 090 16. 7 Cr 0. 010.96 0. 95 0. 97 98. 0 E-Gontaining 2% soda Q 0.012 0.012

ash 11 33 1 0- 110 0- 120 0.010 0 094 10.6 C1 0. 02 0. 99 0. 97 0. 9998. 0 F-Containing no aceel- C 0-0 0011 l. erator 17 75 S1 0- 232 0- 2600.028 0.092 30.4 Cr 0.02 0.98 0. 96 0.98 98. 0

The pronounced efiect of the accelerator in considerably increasing theexothermic power and greatly improving the solubility of the pellets insteel whether the mixtures contained carbon or not is clearlyillustrated. The analytical results show that in the case of thehigh-carbon pellets, C and D, all of the carbon was recovered frompellet D, which contained soda ash, but that carbon recovery from pelletC was incomplete. Moreover, silicon recovery from pellet C was muchgreater than that from pellet D. These observations demonstrate that inthe absence of the accelerator, a portion of the carbon in the pellet isoxidized as taught in the prior art, but that with the acceleratorpresent, silicon alone is oxidized while the carbon remains unafiected.The increased oxidation of silicon in pellets containing no carbon butin the presence of an accelerator is shown by a comparison of the testson pellets E and F.

the oxidation of carbon and the alloying element in the mixture. Theproportion of silicon in the.

grade of ferrochrome-silicon (50% silicon) used in the examples citedwas slightly more than the stoichiometric equivalent of potassiumperchlorate. Little additional improvement in exothermicity was observedwhen the ratio of ferrochrome-silicon to potassium perchlorate wasincreased beyond 1 to l. The form to which the. silicon is present, i.e., whether the silicon is a;

7 to the mechanism described in the prior art by Udy for some ofhisprocesses. However, it is of no importance in the present inventionin view of the much greater effectiveness of the controlledsilicon-potassium perchlorate-soda ash reaction. The present inventionis just as efiective with low-carbon ferro-alloys as shown in Table VI.

8 celeratorfis' present in an amount suflicie'rlt to promote thereaction; the quantities .of silicon, potassium perchlorate andaccelerator being .so' proportioned :to the alloying element that uponignition of themixture in a bath of molten metal suflicient heat isgenerated to counteract the normal chilling tendencies of the alloyingele= 1 Silicon-bearing low-carbon ferrochrome containing approximately5%silicon. Silicon-bearing low'carbon ferrochrome containing approximately9% silicon.

The data of Table VI were obtained from the results of exothermicitytests made as described previously.

Pellets of the last composition listed in Table VI were also usedsuccessfully to add 6% chromium to steel. -A 50-.lb. heat of low-carbonsteel was melted in an induction furnace. The temperature of the heatwas raised to 1650 C., and the power was turned off the furnace. Thepellets were added to the steel with the power on. They dissolved in 25seconds. The heat was held for a minute and a half with the power offand then poured into an ingot mold. It was still quite hot when poured,although a similar amount of plain ferrochromium added in that manner isknown to chill the steel below pouring temperature before the additionis completely dissolved. Chromium recovery was 90%, and there was nosignificant segregation within the ingot.

The potassium perchlorate-silicon-soda ash mixture is also efiective inimproving the solution of ferro-alloys in cast iron where the relativelylow temperatures normally prevailing make solution of alloys such asferrochrome somewhat difficult. Rate-of-solution tests similar tothose-de scribed above in connection with Table I gave the resultslisted in Table VII for cast iron. temperature of the molten cast ironbath was approximately 13"I5 C. at the time of the addition.

TABLE VII The ments contained therein and to increase the rate ofsolubility of said alloying elements.

Accordingly, the mixture may contain between 1% and 15% potassiumperchlorate, at least 0.5% silicon, the atomic ratio of silicon to theoxygen of the potassium perchlorate being 'at least 015, and theaccelerator being present in an amount sufiicient to promote thereaction but not less than 0.5%, the remainder being alloying elements.

In a preferred embodiment of the invention,

the mixture may contain between 3% and 10% potassium perchlorate, atleast 1.2% silicon, the atomic ratio of silicon to the oxygen in thepotassium perchlorate being at least 0.5; between 1% and 5% soda ash,the remainder being alloying elements.

The data in Table VIII, shows the effect of adding ferro-alloys andpellets containing silicon, potassium perchlorate, and soda ash tomolten steel. In this application of the invention the mixture, suitablyin the form of pellets, adds nothing to the molten steel except heat andper- .haps some iron if the silicon is present in the form offerro-silicon. The use of the exothermic pellet in this manner isparticularly advantageous when the production of an exothermic alloysimilar to the exothermic chrome alloy of the invention may not bejustified on economic According to one aspect of the invention, theexothermic mixture comprisesessntially alloying elements, silicon,potassium perchlorate and an accelerator such as Soda ash; thecomponents of the mixture being present in such quantities and being soproportioned that the silicon content is at least sufiicient to combinewith all of the grounds. For example, there is a limited .use atpresentfor an exothermic manganese alloy'suit able for making ladle additionsof manganese. But the net effect of an exothermic manganese alloy can beobtained by adding to a ladle ferro manganese and exothermic pellets ofthe invention containing silicon, potassium perchlorate,

oxygen in the potassium perchlorate, and the ac- 75 and soda ash. V V i9 In Table VIII the data is based on the addition of 1% of an alloyingelement in the form of a ferro-alloy. The additions were made underconditions similar to those and in a furnace of the type describedabove.

TABLE VIII Ratio of Potassium Reac- Temp Composition of Pellets gggg g gg e 2$; D ron,

addition, Seconds grams/lb 56%tP0tassium pcrchlo ra e 1.34% Ferrosilicon(75% Chromium a 25 50 10 silicon 10% Soda Ash 57% Potassium perchlorate.34% Ferrosilicon (50% "do iiii 87 40 10 silico 9% Soda Ash 50% Potassiumperchlorate. 45% Fcrrosilicon (50% do 45 71 16 silicon). Soda Ash I..52%tPotassium perchlora e. 43% Ferrosilicon (50% 15, 16 45 s silicon).5% Soda Ash 54% Potassium perchlorate. 44% Ferrosilicon (50% do 80 43 ssilicon). 2% Soda Ash With an exothermic chromium-containing pellet, aratio of 25 grams of potassium perchlorate per pound of chromium isadequate to permit the addition of one per cent chromium to molten steelwith a temperature drop of about C. It can be seen from Table VIII thata, larger amount of potassium perchlorate is required to eifect thesameaddition of chromium with a comparable heat los when the exothermicpellet doe not contain the chromium.

The exothermic mixture to be used principally for the addition of heatto molten iron and steel should have a minimum soda ash content of 2% ofthe combined weights of the silicon and potassium perchlorate in thepellet. Smaller quantities of soda ash result in an unsatisfactoryreaction rate or in no reaction at all. If too much soda ash is presentin the pellet, there is a possibility that the mixture might be ignitedprematurely, for example, by sparks. In general, no more than five percent soda ash will be required. The silicon and potassium perchlorateshould be present in sufficient quantities to insure a useful exothermicreaction. In general, the mixture should have a minimum silicon contentof Potassium perchlorate should be present in such quantities as toinsure the presence of enough oxygen to react with the silicon ifcontamination of the iron or steel with silicon is to be avoided. Anexcess of oxygen, if present, is not as undesirable as in the case ofthe pellet containing an alloying element since the excess oxygen haslittle or no harmful effects except possibly the oxidation of smallquantities of carbon and iron.

In the mixture of the invention which does not have incorporated thereinan element to be alloyed with iron or steel, best results have beenobtained with the following proportions of mate rials: to 60%ferrosilicon containing at-least 15% silicon, 70% to 40% potassiumperchlorate, and at least 2% soda ash.

A preferred exothermic mixture according tothe invention has thefollowing composition: 54%

10 potassium perchlorate, 44% ferrosilicon (containing 50% silicon), and2% soda ash.

The silicon in the above compositions, including those with as well asthose without an alloying element, may be present in any of a number offorms. For example, it may be present as elemental silicon or asferrosilicon. If alloying elements are present in the composition,silicon may be present as an alloy of silicon with the other alloyingelements.

The method of the invention broadly comprises incorporating alloyingelements in iron or steel by igniting in contact with molten iron orsteel an exothermic mixture consisting essentially of silicon, potassiumperchlorate and soda ash; the components of the mixture being present insuch quantities and being so proportioned that the silicon content is atleast sufiicient to combine with all of the oxygen in the potassiumperchlorate, and the soda ash is present in an amount sufficient topromote the reaction.

It is not necessary that the agents of the invention be pelleted orbriquetted. Loose, unbonded mixtures are also eifective. In general,however, pelleting or briquetting is preferred both for ease in handlingand because, as is well known to the art, compacting such mixturesimproves their efiiciency by reason of closer contact of the activeconstituents. In this respect, the agents of this invention have aparticular advantage because they require no special bonding agent orcritical drying treatment.

The particle size of the comminuted constituents in these agents is notespecially critical. It is a fundamental principle of chemistry,however, that the finer the particle size of the materials in a reactivemixture, the greater the ease with which those materials react, becauseof the increased contact area between the reactants. Moreover, it is oldin the art that fine particle size facilitates pelleting. For the agentsdescribed above, a particle size to pass through a mesh screen for themetallic constituents has been found convenient.

For certain types of prior art exothermic agents, particularly wherereaction between carbon and the oxidizing agent occurs, a high degree ofmixing or special blending, so that each particle of the metallicconstituents is in contact with the oxidizing agent, is said to benecessary. For example, Udy teaches in relation to many of his prior artmixtures the use of an oxidizing agent of the group typified by sodiumnitrate with a reducing agent such as carbon or silicon which may or maynot be a part of the ferro-alloy, the whole essentially being bonded byraising the temperature of the briquetted mass to the fusion point ofthe oxidizing agent and cooling with the result that the particles ofthe briquet are cemented together by the 0xidizing agent.

The agents of the present invention are sufficiently reactive andpowerful that such special techniques are entirely unnecessary. Withthese agents it is only necessary to avoid major segregation of thereactants. This feature leads to more certainty of reaction and enablessubstantial economies in large-scale production of the agents.

The agents of this invention have many other advantages in addition tothose already men tioned. For example, the silicon-potassium perchloratereaction, when controlled as described soda ash, is so eifective thatonly a small amount of the reaction mixture need be added to aferro-alloy in order to gain great improvement in solution of theferro-alloy. This is a definite economic advantage on the basis ofproduction, handling, and transportation costs per unit of ferro-alloy.Furthermore, potassium perchlorate gives up no elements that may produceundesirable contamination in steel as do other oxidizing agents such asnitrates, permanganates, chromates, and manganese dioxide. Nitrates giveoff nitrogen which is harmful in many steels and may be particularlyundesirable in nitrogensensitive steels such as the high-chromiumsteels. Other common oxidizing agents give up' such elements asmanganese and chromium that may not be desirable in certain instances.All of the reaction products of the mixture of the invention escape fromthe steel. Moreover, potassium perchlorate gives off no noxious fumesas, for example, does sodium nitrate which gives ofi oxides of nitrogen.Analyses of the atmosphere over the heatsin some of the tests describedabove have indicated the complete absence of measurable quantities ofany noxious gases. The end products of the agent of the invention are asmall amount of an innocuous silicate slag and potassium chloride whichleaves the metal as a harmless vapor. In addition, it is known tochemical science that potassium perchlorate, although highly reactive,is more stable than the chlorates and, therefore, isless hazardous inhandling and shipping;

Although various types of ferrochromium and ferromanganese were theferro-alloys used in the examples of this invention described in thisspecification, the invention is not limited to these materials. It isequally effective with any ferroalloy, such as ferrovanadium, or anyalloying element such as nickel or copper that is relatively inert anddissolves in steel or iron with the absorption of heat. I

This application is in part a continuation of my copending applicationSerial No. 134,359, filed December 21, 1949, now abandoned.

What is claimed is:

' 1. An exothermic mixture consisting of silicon, potassium perchlorate,and soda ash, said silicon being present in an amount equal to at leastof said mixture, the proportions of silicon and potassium perchlorate insaid mixture being such that the atomic ratio of silicon to the oxygenin the potassium perchlorate is at least i "12 equal to at least 2% ofthe combined weights of silicon and potassium perchlorate the remainderbeing substantially all iron and incidental impurities.

2. An exothermic mixture consisting of ferrosilicon, potassiumperchlorate, and soda ash, said ferrosilicon having a silicon contentsuch that at least 15% of said mixture is silicon, the proportions ofsilicon and potassium perchlorate in said mixture being such that theatomic ratio of silicon to the oxygen in the potassium perchlorate is atleast 0.5, said soda ash being present in an amount equal to at least 2%of the mixture the remainder being incidental impurities.

3. An exothermic mixture consisting 'of 30% to of ferrosilicon having asilicon content such that at least 15% of the mixture is silicon, to 40%of potassium perchlorate, and at least 2% soda ash the remainder beingincidental impurities.

4. An exothermic mixture consisting essentially of 1.5% to 15% potassiumperchlorate, silicon being present in an amount of at least 0.5% and insuch greater amount as is required to provide an atomic ratio of siliconto the oxygen in the potassium perchlorate of at least 0.5, soda ash inan amount between 0.5% and 10%, the remainder being alloying elements.

5. An exothermic mixture as claimed in claim 4 wherein chromium is acomponent of the 2.1-. loying elements.

6. An exothermic mixture consisting essentially of 3% to 10% potassiumperchlorate, silicon being present in an amount of at least 1.2% and insuch greater amount as is required to provide an atomic ratio of siliconto the oxygen in the potassium perchlorate of at least 0.5, between 1%and 5% soda ash, the remainder being alloying elements.

' DONALD C. HILTY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,280,873 Udy Apr. 28, 1942FOREIGN PATENTS Number Country Date 581,888 Great Britain Oct. 29, 1946

1. AN EXOTHERMIC MIXTURE CONSISTING OF SILICON, POTASSIUM PERCHLORATE,AND SODA ASH, SAID SILICON BEING PRESENT IN AN AMOUNT EQUAL TO AT LEAST15% OF SAID MIXTURE, THE PROPORTIONS OF SILICON AND POTASSIUMPERCHLORATE IN SAID MIXTURE BEING SUCH THAT THE ATOMIC RATION OF SILICONTO THE OXYGEN IN THE POTASSIUM PERCHLORATE IS AT LEAST 0.5, SAID SODAASH BEING PRESENT IN AN AMOUNT EQUAL TO AT LEAST 2% OF THE COMBINEDWEIGHTS OF SILICON AND POTASSIUM PERCHLORATE THE REMAINDER BEINGSUBSTANTIALLY ALL IRON AND INCIDENTAL IMPURITIES.